JP3491642B2 - Optical fiber preform, optical fiber, and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber preform, an optical fiber and a method for manufacturing them.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a quartz optical fiber, a VAD method, an external attachment method, an internal attachment method (MCVD, plasma CVD method), a rod-in-tube method, a double crucible method, etc. are known. There is. These typical processes are described below. In the VAD method, a raw material is supplied to an oxyhydrogen burner, glass fine particles are synthesized by a hydrolysis reaction in a flame, and the fine glass particles are attached to the tip of a rotating starting rod and grown in an axial direction to form a porous matrix Created, dehydrated, made transparent, reduced diameter,
It is stretched to form a columnar optical fiber preform. Then
This is a method for producing an optical fiber having a desired refractive index distribution by drawing a base material for this optical fiber. In the internal attachment method, a raw material and oxygen are sent to the inside of a quartz tube, and a glass thin film is laminated inside by reciprocating a burner from the outside, and solidified into a preform for an optical fiber. This is a method of drawing an optical fiber by drawing the obtained base material (information transmission fiber, fiber and industry Vol.4 No.5 1985, p.151-160). In the rod-in-tube method, a glass rod (rod) that serves as a core is inserted into a thick glass tube (tube) that serves as a clad, and its lower end is sealed, softened by heating, pulled, and simultaneously drawn to produce an optical fiber. Is a method of manufacturing.

[0003]

The conventional manufacturing process of a base material for an optical fiber is considered so that the refractive index distribution becomes concentric in any sectional structure of the optical fiber obtained after drawing. . However, in reality, the cross-sectional structure of the core or clad in an optical fiber is slightly elliptical or distorted circle,
The refractive index distribution is no longer perfectly concentric. This causes a difference in group velocity between two orthogonal polarized waves in the cross section of the optical fiber, resulting in a large polarization dispersion. Therefore, when it is put into practical use as an optical fiber for a submarine cable and a trunk cable, which requires a large capacity and long distance transmission, the influence of polarization dispersion becomes significant. However, if the manufacturing process of the optical fiber is strictly controlled, it is possible in principle to make the core into a perfect circle or to form the clad and the core into concentric circles. However, the more rigorous the process control is, the more difficult it is and the higher the cost is. In addition, it is impossible to realize an optical fiber that is completely circular and concentric even if it is possible in principle, but it is impossible because the ideal manufacturing process cannot be controlled in practice. After all, polarization dispersion due to structural distortion cannot be avoided.

Therefore, the present invention aims to provide an optical fiber capable of equivalently suppressing polarization dispersion caused by the optical fiber and the core even when the optical fiber and the core are not perfectly circular or concentric. And

Another object of the present invention is to provide an optical fiber preform suitable for manufacturing such an optical fiber, and a suitable manufacturing method thereof.

[0006]

Optical fiber preform according to the problem-solving means for the present invention includes a core made of a transparent material of the central portion is constituted by a cladding made of a transparent material in the peripheral portion, the central axis or which
It is twisted uniformly in one direction around an axis parallel to, and has a length equal to or greater than the pitch of the twist.

Further, the optical fiber according to the present invention is made into a fibrous form by heating and softening the above-mentioned optical fiber preform from the end and drawing the fiber, and a unidirectional and uniform twist remains. And having a length equal to or greater than the pitch of the twist.

The method of manufacturing the optical fiber preform according to the present invention has various modes corresponding to the conventionally known manufacturing methods described above.

A method of manufacturing an optical fiber preform according to a first aspect includes a first step of preparing a preform having a core made of a transparent material in a central portion and a clad made of a transparent material in a peripheral portion, A second step of heating and softening the base material while applying reverse rotational stress to the base material from both ends thereof and rotating the base material at least once around the central axis or an axis parallel thereto. It is characterized by being provided.

In the method of manufacturing an optical fiber preform according to the second aspect, a preform having a core made of a transparent preform in the central portion and a layer of a porous material to be a clad in the peripheral portion is prepared. Step 1 and applying reverse rotational stress to the core from both ends to rotate the core material once or more around the central axis to heat the base material to make the layer of the porous material transparent and the core. And a second step of softening.

In the method for manufacturing an optical fiber preform according to the third aspect, a preform having a layer of a porous material to be a core in the central portion and a clad made of a transparent material in the peripheral portion is prepared. Step, and while applying reverse rotational stress to the clad from both ends to rotate it about the central axis one or more times, heat the base material to soften the clad and make the porous material layer transparent. And a second step of

In any of the above first to third aspects, the second step may heat the base material while applying tensile stress in the direction of the central axis together with reverse rotational stress. Further, in the second step, the base material may be sequentially heated from one end side to the other end side.

[0013] In the first and second embodiment, in a first step, the outer periphery of the base material for the core noncircularity 0.5
It may be characterized in that the optical fiber preform is formed by using the ground preform for core after grinding so as to be not more than% .

According to the method of manufacturing an optical fiber of the present invention, one end of the optical fiber preform manufactured by any one of the above-mentioned first to third aspects is held and the other end is positioned downward. The optical fiber preform is then drawn, and then the optical fiber preform is heated from the other end to be softened, whereby the optical fibers are sequentially drawn.

In the method of manufacturing an optical fiber according to the present invention, while rotating the optical fiber preform, one end of the optical fiber preform manufactured by any one of the above-mentioned first to third aspects is manufactured. It may be characterized in that the optical fiber is drawn in sequence by holding and holding it to hang it so that the other end is located below, and then heating and softening the optical fiber preform from the other end.

[0016]

The optical fiber according to the present invention is twisted in one direction and uniformly around the central axis. Therefore, even if the cross-sectional structures of the optical fiber and the core are not perfect circles and concentric circles, the distortion on the cross-sectional structure appears uniformly in each direction of 360 degrees at a constant pitch (twisting pitch). The entire long optical fiber equivalently functions as an optical transmission line having a true circle and a concentric circle structure. Therefore, the polarization dispersion generated in the optical signal propagating through the optical fiber having a length equal to or greater than the pitch of the twist appears one after another in the direction of 360 degrees around the optical axis and is canceled one after another (that is, two polarizations). (The wave modes can be easily combined), and as a result, the overall polarization dispersion can be suppressed.

Since the optical fiber preform according to the present invention is preliminarily twisted in a fixed direction and uniformly, it works so as to realize the above optical fiber only by drawing from the end.

The method for producing an optical fiber preform according to the first aspect applies a twist to a preform which is already transparent and has a core and a clad integrated therein. Such a transparent preform is VAD. By heating and making the porous base material transparent by the internal method, or by heating and making the porous layer on the outside (cladding side) of the base material by the external attachment method, or inside the basic material by the internal attachment method. It is obtained by heating and making the porous layer on the (core side) transparent, or by heating and integrating a transparent rod material (core material) and a transparent tube material (clad material) by the rod-in-tube method. Then, by heating and softening while applying rotational stress, the twist necessary for suppressing polarization dispersion when an optical fiber is formed on the base material is added. Further, the process can be shortened by adding a twist together with the solidification process after the inner core layer is made transparent by the internal attachment method.

The method for producing an optical fiber preform according to the second aspect is one in which the step of making the cladding of the preform by an external attachment method transparent and the step of applying a twist to the preform are carried out simultaneously. In this method, the step of making the core of the base material transparent by the internal attachment method and the step of twisting the base material are performed at the same time, and the steps can be shortened.

In any of the first to third aspects, if the tensile stress is applied together with the rotational stress, the base material can be reduced in diameter and stretched at the same time.

In the first step of the first and second aspects, the outer circumference of the base material for the core has a non-circularity of 0.5 % .
After grinding as described below , by forming the optical fiber preform by using the ground preform for core, it is possible to reduce the amount of twist required for improving polarization dispersion.

The optical fiber of the present invention can be obtained by drawing the optical fiber preform obtained by the manufacturing method of the first to third aspects. That is, when the twisted base material is heated and softened from the end and drawn, the twist remains in the optical fiber. In this drawing, if the optical fiber preform is rotated, the amount of twist of the core in the optical fiber state can be increased.

In any of the above inventions, an optical fiber having a spiral core can be obtained by drawing a base material in which the center of twist is particularly located outside the core (cladding portion). An optical fiber having a spiral core can be a circular polarization maintaining optical fiber by adjusting the pitch of the spiral.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the outline of the principle of the present invention will be described.

Assuming that the cross-sectional shape of the core is an ellipse, the non-circularity (e) of the ellipse is defined by e = ((maximum outer diameter)-(minimum outer diameter)) / (average outer diameter) Non-circularity (e) of ellipse and polarization dispersion (PM
The relationship with D) is "K. Kashihara et al., Internationa
l Wire & Cable Symposium Proceeding 1993, pp635-63
8 ". Then, the polarization dispersion (PMD) is improved by twisting the core as follows: PMD (φ) / PMD (φ = 0) = (2π / 2φ) (B / λ) (1) where φ: optical fiber It is known that the twisting speed of the core per unit length B: birefringence of optical fiber λ: wavelength of light (AJBarlow et al.: APPL
IED OPTICS, Vol.20, No.17,1 September 1981, pp2962
-2968). In a normal optical fiber, B = 1
It is about 0 ^-5 to 10 ^-7 .

The non-circularity of the core of the optical fiber preform is usually increased in the drawing step when forming the optical fiber. The inventor measured the polarization dispersion value after increasing the non-circularity and making the optical fiber by an experiment, and according to (1), the polarization dispersion value =
The twist pitch length of the core in the optical fiber state required to obtain about 0.1 ps / km ^1/2 was determined. The results are shown in Table 1.

[0027]

[Table 1]

Since the non-circularity in the optical fiber preform is 5% or less, from Table 1, the twist pitch length of the core in the optical fiber state is 1 cm or more and 10 cm or more depending on the non-circularity in the optical fiber preform.
It should be 0 m or less. The outer diameter of such twist pitch length of the core of an optical fiber state (L ₀₎ twist pitch length of the core in the optical fiber preform for realizing an (L ₁₎ is generally of the optical fiber is 0.125mm Therefore, L ₁ = (0.125 / D) ² · L ₀ (2) Here, D is determined by the outer diameter (unit: mm) of the optical fiber preform.

In addition, the non-circularity of the normally manufactured optical fiber preform is 2% or less, and in view of the ease of twisting in the optical fiber preform, the twist pitch length of the core in the optical fiber state is , 10c depending on the non-circularity in the optical fiber preform
It is realistic to set the distance to m or more and 50 m or less.

If a method of grinding the outer circumference of the core preform is used to reduce the non-circularity of the core of the optical fiber preform,
By grinding the outer circumference, the non-circularity of the core of the optical fiber preform was reduced to 0.
It can be controlled to 5% or less. In this case,
The twist pitch length of the core in the optical fiber state can be set to 1 m or more and 50 m or less depending on the non-circularity of the optical fiber preform.

Further, the inventor conducted an experiment on the improvement of the polarization dispersion value by using a twisted optical fiber preform and drawing it while rotating the optical fiber preform.
The results are shown in Table 2.

[0032]

[Table 2]

As shown in Table 2, although the substantial twist pitch (converted in the optical fiber state) is the same,
The polarization dispersion value decreased as the rotation speed during drawing increased. This means that the optical fiber has a non-circularity that is higher than the non-circularity of the optical fiber preform by ordinary drawing, and the reason is that the temperature distribution inside the heating furnace at the time of drawing is due to the optical fiber preform. It is considered that this is due to unevenness in the radial direction. It is presumed that this temperature unevenness causes temperature unevenness in the radial direction of the optical fiber preform to increase the non-circularity. Therefore, in addition to the effect of improving the polarization dispersion value due to the effect of twisting due to rotation, the rotational drawing also suppresses the increase in non-circularity due to the reduction in radial temperature unevenness of the optical fiber preform due to rotation. It is presumed that the improvement effect will be exhibited.

Hereinafter, an optical fiber preform, an optical fiber and a method for manufacturing them according to an embodiment of the present invention will be sequentially described with reference to the accompanying drawings.

FIG. 1 is a diagram showing a perspective structure of a part of an optical fiber preform according to an embodiment and a sectional structure on four planes A to D. The optical fiber preform 1 is composed of a clad preform 11 made of silica glass and a high-refractive-index core preform 12 provided at the center thereof. Here, it is assumed that the core preform 12 is located at the center of the optical fiber preform 1 but has a convex portion 13 instead of a perfect circular shape.

Since the optical fiber preform 1 of this embodiment is uniformly twisted in a fixed direction, assuming that the central axis of the twist is the center of the core preform 12, the planes A to D in FIG. The cross section at is as outlined by the arrow in the figure. That is, the convex portion 13 of the core preform 12 is the optical fiber preform 1
As the axial position of moves to A, B, C, D, it rotates around the central axis. That is, the core preform 12 having the protrusions 13 is also twisted according to the twist of the optical fiber preform 1.

When the optical fiber preform 1 of FIG. 1 is set in a drawing furnace and the lower end is heated to draw the optical fiber, this twist remains in the obtained optical fiber. For this reason,
If twisted more than once in the entire length of the optical fiber,
The distortion of the core of the optical fiber corresponding to the structural distortion of the core preform 12, which is the convex portion 13, appears in all directions of 360 degrees around the central axis. For this reason, the polarization dispersion of the propagating light due to the distortion is canceled as a whole by facilitating the coupling of the two polarization mode lights, and equivalently functions as a perfect circle and a concentric optical fiber. .

There are various modes regarding the structural strain of the core base material 12 and the position of the central axis of torsion, and these are shown in FIGS. 2A to 2D show a case where the core base material 12 has an elliptical shape and the center of the core is twisted to be the central axis (the position where the alternate long and short dash line intersects), and the plane A of FIG.
It is sectional drawing in -D. 2E to 2H are also cross-sectional views of planes A to D, the core preform 12 has a distorted circular shape, and the torsion center axis is slightly deviated from the center of the core preform 12.

FIG. 3 shows the case where the core base material 12 is substantially circular, and FIGS. 3A to 3D show the case where the twist center is the end of the core base material 12. , (E) of FIG.
(H) is the case where the twist center is off the core base material 12 and is inside the clad base material 11. In these cases as well, due to the fact that the clad thickness of the drawn optical fiber is different and is not concentric, polarization dispersion becomes a problem if there is no twist.
If there is more than one twist, it is canceled and the overall polarization dispersion is suppressed.

When the core base material 12 is eccentric as shown in FIG. 3, particularly when it is relatively eccentric as shown in FIGS. 3E to 3H, this is drawn. The optical fiber not only facilitates coupling of two polarization modes and suppresses polarization dispersion, but also exhibits the following special action. That is, an optical fiber having a spiral core can be obtained by drawing a base material in which the center of twist is particularly located outside the core (cladding portion). An optical fiber having a spiral core can be a circular polarization maintaining optical fiber by adjusting the pitch of the spiral.
Further, in an optical fiber having a spiral core, since the substantial length of the core (the length of the optical transmission line) is longer than the actual length of the optical fiber, rare earth elements or the like are added to such an optical fiber. By producing a doped optical fiber amplifier, an optical fiber amplifier having the same performance can be obtained by using a shorter optical fiber than a conventional optical fiber amplifier.

Next, embodiments of the respective methods for producing the optical fiber preform and the optical fiber according to the present invention will be described.

FIG. 4 is a diagram for explaining a manufacturing process using the VAD (axising) method. As shown in FIG. 3A, the starting rod 21 made of quartz glass is fixed to the rotary chuck 22, and the soot base material 4 is manufactured using the burners 3A and 3B. Here, a raw material having a high refractive index for the core is supplied to the burner 3A, and a raw material having a low refractive index for the clad is supplied to the burner 3B. That is, SiCl ₄ , GeCl ₄ ,
When a glass source gas such as POCl ₃ is introduced into the oxyhydrogen flame, the next hydrolysis reaction proceeds at 500 to 800 ° C. SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl GeCl ₄ + 2H ₂ O → GeO ₂ + 4HCl POCl ₃ + 3 / 2H ₂ O → 1 / 2P ₂ O ₅ + 3H
The fine glass particles produced in the Cl flame are sprayed onto the tip of the starting rod 21, adhered and deposited, and the porous soot base material 4 is formed.
Is formed. The soot base material 4 is pulled up in accordance with the growth rate in the axial direction. In the step of FIG. 4B, the starting rod 21 is fixed by the chuck 24, and the soot base material 4 is inserted from the lower end.
Is passed through a heating furnace 23 to obtain a vitrified transparent optical fiber preform 1.

Next, as shown in FIG. 4C, the dummy rod 25 is fusion-bonded to the optical fiber preform 1 and the starting rod 21.
(Or another dummy rod fused again) to the rotary chuck 26A and the dummy rod 25 to another rotary chuck 26A.
It is fixed to B and the optical fiber preform 1 is sequentially passed through the heating furnace 23 from one end to the other end to be softened. At this time, by rotating the rotating chucks 26A and 26B in opposite directions, the optical fiber preform 1 is twisted from the softened portion. Further, by moving the rotary chucks 26A and 26B in directions away from each other, the optical fiber preform 1 is stretched and reduced in diameter.

Next, as shown in FIG. 4D, the dummy rod 25 is removed from the optical fiber preform 1 and the starting rod 21 is removed.
Is fixed to the chuck 27 and set in the drawing furnace, and the lower end is heated by the heater 28 to draw the optical fiber 19. The drawn optical fiber 19 is coated with a coating material and wound on a drum 29. This optical fiber 19
Has the twist that the optical fiber preform 1 had. Here, the chuck 27 is not limited to a fixed chuck, but may be a rotary chuck. When the chuck 27 is a rotary chuck, the dummy rod 25 is removed from the optical fiber preform 1, the starting rod 21 is fixed to the chuck 27, set in the drawing furnace, and the chuck 27 is rotated.
While rotating the optical fiber preform 1, the lower end is heated by the heater 28 to draw the optical fiber 19.

The process of twisting the optical fiber preform 1 may be added to the conventional manufacturing process. However, as in the above-mentioned embodiment, the diameter reduction / formation for forming the preform for drawing is performed.
It may be twisted while being stretched in the stretching step, which is advantageous in terms of cost.

When twisting the base material, it is preferable to rotate the chucks at both ends supporting the base material in opposite directions as in the above embodiment. By doing so, the number of rotations can be suppressed, so that when a misalignment occurs, the base material does not bend due to centrifugal force.

In particular, when a horizontal glass lathe is twisted by the above method, the base material may be deformed. That is, by rotating the chucks at both ends in opposite directions, the rotation of the heating and softening portion is slowed down, so that uniform heating cannot be performed over the entire circumference, and the heating softening portion sags by its own weight. Therefore, in the case of the horizontal type, it is preferable to rotate both chucks in the same direction and change the number of rotations. Further, it can be used in the case of a vertical type for the purpose of heating more uniformly over the entire circumference.

FIG. 5 is a diagram showing a manufacturing process using the internal attachment method. First, the quartz tube 15 is prepared, and the raw material gas is supplied to the inside of the quartz tube 15 while rotating and heating from outside with the oxyhydrogen burner 31. As the raw material gas, for example,
SiCl ₄ , GeCl ₄ , POCl ₃ , BBr ₃ , O ₂
When these glass raw materials are fed, the following thermal oxidation reaction occurs. SiCl ₄ + O ₂ → SiO ₂ + 2Cl ₂ GeCl ₄ + O ₂ → GeO ₂ + 2Cl ₂ POCl ₃ + 3 / 4O ₂ → 1 / 2P ₂ O ₅ +3/2
Cl ₂ BBr ₃ + 3 / 4O ₂ → 1 / 2B ₂ O ₃ + 3 / 2B
r ₂ As a result, the generated glass particles such as SiO ₂ adhere to the inside of the quartz tube 15 to form the core porous layer 41.

Next, both ends of the quartz tube 15 are attached to the rotary chuck 2.
6A and 6B (one end of the quartz tube 15 may be heated and sealed and then fixed), and the quartz tube 15 is twisted while being passed through a heating furnace 23 (or a burner) while heating. As a result, solidification, transparent vitrification, and addition of twist can be performed at the same time. If the rotary chucks 26A and 26B are moved in the separating direction, stretching and diameter reduction can be performed at the same time.

In the manufacturing method including the step of solidifying such a glass pipe, the cross section tends to be elliptical in the solidifying process, and the polarization dispersion tends to become large. The effect of further improving polarization dispersion can be obtained. Further, if the glass is made transparent while twisting in the solidification process, the manufacturing cost is almost unchanged. However,
If the manufacturing cost is ignored, solidification, transparent vitrification, twisting, and stretching can be performed in separate steps.

Next, as in the case of FIG. 4 (d), the fiber is set in a drawing furnace and drawn, whereby an optical fiber with a residual twist is obtained. In the step of depositing the glass particles on the inner surface of the quartz tube 15, the raw material for the clad is introduced to form the porous layer in the first step, and then the raw material for the core is introduced and separated in the second step. If the porous layers are stacked, the core and the clad can both be glass synthesized by flame hydrolysis.

FIG. 6 shows a manufacturing process using an external method. First, a quartz glass rod that serves as the base material 12 for the core is prepared, and is exposed to the flame containing the glass particles from the burner 3 while rotating the same (see FIG. 6A).
Then, the porous layer 41 to be the clad is formed outside the core base material 12. The core base material 12 may be formed by grinding the outer periphery of the original core base material into a substantially circular shape.

Next, this is fixed to the rotary chucks 26A and 26B, and the porous layer 41 is vitrified and twisted at the same time. If the preform is heated while applying a tensile stress as well as a reverse rotational stress, vitrification, twisting, and stretching are performed simultaneously (see FIG. 6 (b)).
Finally, the obtained optical fiber preform is set in a drawing furnace at the same time as in FIG. 4 (d) and drawn from the lower end to obtain an optical fiber with residual twist.

FIG. 7 is a diagram showing a manufacturing process using the rod-in-tube method. In this case, the pipe-shaped clad base material 11 and the rod-shaped core base material 12 are prepared in advance, and the core base material 12 is inserted into the through hole 16 of the clad base material 11 (see FIG. )reference). At this time, if the through hole 16 is eccentric, the above-mentioned spiral core optical fiber having a spiral radius according to the amount of eccentricity can be obtained. The base material 11 can be manufactured by the VAD method or the like. The core base material 12 may be formed by grinding the outer periphery of the original core base material into a substantially circular shape.

Then, the preform 11 for the cladding and the preform 12 for the core are fused at one end to form an integrated preform.
The frames are fixed to the rotary chucks 26A and 26B, and they are integrated in the heating furnace 23 from one side while applying reverse rotational stress (see FIG. 7B). Similar to the above-mentioned examples, if tensile stress is further applied, the integration, the twist addition and the stretching can be performed in a single step.

Finally, by drawing in the same manner as in FIG. 4 (d), an optical fiber with a twist remaining can be obtained. In the method of this embodiment, the spiral radius of the core is set by the amount of eccentricity of the through hole 16 so that the length of the core (substantial optical transmission line length) is different from the actual length of the optical fiber itself. Since it can be set, it is suitable for applications such as the above-mentioned optical fiber amplifier.

Next, a concrete example of the present invention will be described.

Example 1 Dummy rods were fusion-bonded to both ends of a transparent base material (outer diameter 25 mm, length 400 mm), and the lower end was heated in a vertical heating furnace having a hole penetrating in the vertical direction. It was inserted to the height of the upper end of the furnace. The transparent base material was supported by fixing dummy rods to rotatable chucks provided at the top and bottom of the heating furnace. The temperature of the heating furnace was raised to 1900 ° C., and while lowering the upper chuck and the lower chuck at a speed of 1 mm / min, they were rotated at 50 rpm in opposite directions to traverse 400 mm. Then, the transparent base material was drawn into an optical fiber. The polarization dispersion characteristic of the obtained optical fiber is 1.5.
0.05P in 1km fiber with 5μm signal light
It was good with S.

(Example 2) Further, the same transparent base material as in Example 1 was inserted into a heating furnace heated to 1900 ° C, and the upper chuck was 3 mm / min and the lower chuck was 5 mm / min, respectively. While lowering, the lower chuck was rotated at a rotation speed of 15 rpm without rotating the upper chuck, and the transparent base material was stretched while being twisted. The obtained base material had no abnormal appearance and was well stretched to an outer diameter of 19.44 mm.

Example 3 A quartz pipe (outer diameter 30 mm,
Inner surface (inner diameter 10 mm, length 300 mm) was attached to a horizontal glass lathe base material on which a glass layer to be the core was formed, and both ends of the base material were fixed while heating sequentially with an oxygen hydrogen burner from the ends. One of the chucks on both ends
Then, while rotating the other at 20 rpm in the same direction, 5 m
Both chucks were traversed at a speed of m / min. Furthermore, the pressure inside the pipe was reduced to 0.9 atm, and the pipe was solidified by twisting it from the end portion of the base material. The solidified base material was good with no abnormal appearance or bubbles.

Example 4 A horizontal glass lathe was obtained by fusion-bonding dummy rods to both ends of a transparent base material (outer diameter 40 mm, length 100 mm) consisting of a core portion and a clad portion. Attached to. 4 for one of the chucks on both ends
Rotate at 0 rpm, traverse the other at 10 rpm in the same direction as one chuck and traverse at a speed of 40 mm / min, traverse the burner at a speed of 5 mm / min in the opposite direction to the traverse direction of the other chuck. And stretched to an outer diameter of 10 mm. Then, glass microparticles were deposited on the outer periphery of the base material to sinter and make transparent, thereby forming an optical fiber base material. Next, similarly to Example 1, the optical fiber preform was inserted into a vertical heating furnace having a hole penetrating in the vertical direction so that the lower end of the optical fiber preform was at the height of the upper end of the heating furnace. The optical fiber preform was supported by fixing a dummy rod to rotatable chucks provided on the upper and lower parts of the heating furnace. The temperature of the heating furnace was raised to 1900 ° C., and while lowering the upper chuck and the lower chuck at a rate of 10 mm / min, they were rotated at 30 rpm in opposite directions to traverse. After that, the optical fiber preform 3
While rotating at 0 to 500 rpm, an optical fiber was formed by drawing at 100 m / min. 20 for the obtained optical fiber
The core was twisted at a pitch of cm to 2.4 m.

[0062]

As described above, according to the optical fiber of the present invention, the optical fiber is twisted uniformly in one direction around the central axis, and the distortion in cross-sectional structure is 360 at a constant twist pitch.
In the optical signal propagating through the optical fiber, it becomes easy to couple the two polarization modes, and as a result, the overall polarization dispersion can be suppressed equivalently.
In addition, since the optical fiber preform of the present invention is twisted in a fixed direction and uniformly in advance, it is possible to equivalently suppress the entire polarization dispersion as shown above just by drawing from the end. Can be an optical fiber.

Further, according to the optical fiber preform manufacturing method of the present invention, the optical fiber preform obtained by combining the transparent material or porous material in the central portion and the transparent material or porous material in the peripheral portion is transparent. When reducing or reducing the diameter / stretching,
Since the opposite rotational stress is applied to both ends around the central axis, the optical fiber preform after the process is twisted uniformly in a fixed direction and its pitch becomes constant. The twist remains on the fiber,
It may have the above properties. If you draw an optical fiber preform whose center of twist is outside the core,
A circular polarization maintaining optical fiber can be obtained by adjusting the pitch of the helix. As a result, an optical fiber preform suitable for manufacturing the above-described optical fiber and a suitable manufacturing method thereof can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a perspective structure of a part of an optical fiber preform according to an example and a sectional structure on four planes A to D.

2 (a) to (d) are views showing a case where the core base material has an elliptical shape and the center of the core is the twist center axis;
(E) to (h) show the case where the core base material has a distorted circular shape and the twist center axis is slightly deviated from the center of the core base material, and (a) to (d) and (e). 1) to (h) all correspond to the cross-sectional views of planes A to D in FIG.

3 (a) to 3 (d) are views showing a case where the core base material has a substantially circular shape and a twist center axis is near an end portion of the core base material, and FIGS. (h) is a diagram showing a case where the core base material is substantially a circular shape and the center axis of the twist is off the core base material to be in the clad base material,
All of (d) and (e) to (h) are plane A to FIG.
It corresponds to the sectional view of D.

FIG. 4 is a diagram illustrating a manufacturing process using VAD (axising method).

FIG. 5 is a diagram illustrating a manufacturing process using an internal attachment method.

FIG. 6 is a diagram illustrating a manufacturing process using an external attachment method.

FIG. 7 is a diagram illustrating a manufacturing process using a rod-in tube.

[Explanation of symbols]

1 ... Optical fiber base material 3, 3A, 3B, 31 ... Burner,
4 ... Soot base material, 11 ... Clad base material, 12 ... Core base material, 13 ... Convex part, 15 ... Quartz tube, 16 ... Through hole, 19
... optical fiber, 21 ... starting rod, 22, 24, 26A, 2
6B ... Rotating chuck, 23, 28 ... Heating furnace, 25 ... Dummy rod, 27 ... Chuck, 29 ... Drum, 41 ... Porous layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Yokota, 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd. Yokohama Works (56) References International Publication 83/00232 (WO, A1) (58) Survey Areas (Int.Cl. ⁷ , DB name) C03B 37/00-37/16

Claims (15)

(57) [Claims] 1. A core composed of a transparent material in the center and a clad composed of a transparent material in the peripheral portion, and
Alternatively, the optical fiber preform is characterized in that it is twisted uniformly in one direction around an axis parallel thereto and has a length equal to or greater than the pitch of the twist. 2. A first step of preparing a base material having a first transparent material having a central core portion and a second transparent material having a peripheral cladding portion; in addition the rotation stress of the respective opposite directions and the one end and the other end against the timber, the central axis or its parallel
An optical fiber comprising a second step of heating and softening the base material while rotating the one end and the other end about the axis relatively once or more. Base material manufacturing method. 3. A first step of preparing a base material having a glass layer to be a core in a central portion and a portion made of a transparent material to be a cladding in a peripheral portion; While applying rotational stress in opposite directions to the end and the other end, respectively, while rotating the one end and the other end relative to each other about the central axis one or more times, the mother A second step of heating and softening the material and solidifying the base material. 4. The second step is a step of heating and softening the base material while applying the reverse rotational stress and the tensile stress in the central axis direction. The method for producing an optical fiber preform according to 1. 5. A first step of preparing a base material having a transparent material having a central core portion and a porous material serving as a peripheral clad; Applying rotational stress in opposite directions to one end and the other end, respectively, and to the central axis or parallel to this.
While it is rotating and the one end portion and the other end portion and the relatively least once around a shaft, to soften the transparent material with is transparent to the porous material by heating the preform A second step, and a method for manufacturing an optical fiber preform. 6. The second step comprises heating the base material to make the porous material transparent and applying the transparent material while applying the reverse rotational stress and the tensile stress in the central axis direction. The method for manufacturing an optical fiber preform according to claim 5, which is a step of softening. 7. A first step of preparing a base material having a porous material having a central core portion and a transparent material having a peripheral clad, and one of the transparent material and the transparent material. in addition the rotation stress of the respective opposite the end of the the other end, a central axis or parallel thereto
While rotating the one end and the other end relative to each other about one axis at least once, the base material is heated to soften the transparent material and the layer of the porous material is transparent. And a second step of making the optical fiber preform. 8. The second step comprises heating the base material to heat the porous material to make it transparent while applying the rotational stress in the opposite direction and the tensile stress in the central axis direction. 8. The step of softening the transparent material.
A method for manufacturing the optical fiber preform described above. 9. An optical fiber preform manufactured by the method according to claim 2, wherein one end of the optical fiber preform is held and the other end of the optical fiber preform is hung down, While sequentially rotating the optical fiber preform with the central axis of the optical fiber preform as the central axis, sequentially heating the optical fiber preform from the other end to soften the optical fiber preform, thereby sequentially drawing the optical fibers. And a method for manufacturing an optical fiber. 10. The method for producing an optical fiber according to claim 9, wherein the pitch of the twist of the core in the optical fiber produced by drawing is 1 cm or more and 100 m or less. 11. The first step is to prepare a core base material made of a transparent material, and grind the outer periphery of the core base material to make a non- base material.
3. The light according to claim 2, which is a step of arranging the core base material ground in the central portion and a clad base material made of a transparent material in the peripheral portion after setting the circularity to 0.5 % or less . Manufacturing method of fiber preform. 12. The first step comprises disposing a clad base material made of a transparent material on the periphery of a core base material made of a transparent material, and then grinding the outer periphery of the clad base material to reduce the non-circularity.
0. The method of manufacturing an optical fiber preform according to claim 2, characterized in that the step of 5% or less. Wherein said first step includes providing a core preform made of a transparent material, non by grinding the outer periphery of the core preform
The optical fiber mother board according to claim 5, which is a step of forming a layer of a porous material to serve as a clad on the peripheral portion of the ground preform after grinding to a circularity of 0.5 % or less . Method of manufacturing wood. 14. An optical fiber preform manufactured by the method according to any one of claims 11 to 13 is held so that one end thereof is held and the other end is hung down, and then the While sequentially rotating the optical fiber preform with the central axis of the optical fiber preform as the central axis, sequentially heating the optical fiber preform from the other end to soften the optical fiber preform, thereby sequentially drawing the optical fibers. And a method for manufacturing an optical fiber. 15. The method for producing an optical fiber according to claim 9, wherein the pitch of the twist of the core in the optical fiber produced by drawing is 1 m or more and 50 m or less.